This invention relates to charge plates for use in a laminated coating head of the general type described in Beam et al. U.S. Pat. No. 3,586,907, and more particularly to an improved method of connecting electrical leads to charge electrodes in such charge plates.
As explained in copending application Ser. No. 912,495, coating heads of the type described by Beam et al. are used in ink jet printing systems, which create printed matter by selective charging, deflecting, and catching of drops produced by one or more rows of continuously flowing ink jets. The jets themselves are produced by forcing ink under pressure through a series of orifices in an orifice plate, which is one component of the laminated head.
A stimulation arrangement stimulates the jets to break the ink up into uniformly sized and regularly spaced drops, with drop formation occurring in all jets at more or less fixed positions, all located approximately the same distance from the orifice plate. The charge plate is positioned within the coating head so that electrical charging of selected ones of the drops being generated is achieved.
A charge plate of the type used by the Beam et al. patent utilizes a plate of dielectric material provided with a series of charging tunnels located equidistantly along a straight line. Each charging tunnel is coated with an electrically conductive material which defines a cylindrical charging electrode. Electrical leads must be connected to each such charge electrode, and the electrical leads in turn are selectively activated by an appropriate data processing system.
Typical prior art charge plates including such electrodes are disclosed in Solyst, U.S. Pat. No. 3,975,741, in Kuhn, U.S. Pat. No. 3,984,843, and in Bassous et al., U.S. Pat. No. 4,047,184. The prior art also includes charge plates having charging electrodes formed in notches along the edges of the plate, as disclosed in the above mentioned Solyst patent, and also in Robertson, U.S. Pat. No. 3,604,980, Culp, U.S. Pat. No. 3,618,858, and in Van Breemen et al., U.S. Pat. No. 4,035,812.
In addition to the difficulties arising in the fabrication of charge plates, described in detail in copending application Ser. No. 912,495, difficulties have also arisen in reliably and rapidly connecting electrical leads to each individual charge electrode on the charge plate. Previous methods for connecting the electrical leads to each charge electrode used laborious and slow hand painting, with conductive paint, of a connecting line between each lead and charge electrode. The difficulty of such an operation will be appreciated when it is remembered that the center-to-center spacing of each charge electrode is only about 0.423 mm and each charge electrode has an internal diameter of only about 0.355 mm, leaving a spacing between charge electrodes of only about 0.068 mm. Depending upon the size of the charge plate and the area to be printed, anywhere from several hundred to over one thousand connections per charge plate must be made. The previous methods suffered not only from the length of time required to complete the operation, but also from globbing of the conductive paint over into charge electrode tunnels and partially blocking them and irregularities in the conductive connecting lines being painted. This resulted in either a poor or no connection on the one hand to two or more connections flowing into one another on the other.
Accordingly, the need exists in the art for a rapid and reliable method for connecting electrical leads to charge electrodes on a charge plate.